From WO 2010/017903 A1 a separation device for separating solid and/or liquid particles out of a gas flow is known, which is employed with an internal combustion engine in order to separate oil particles and soot particles out of a blow-by gas stream. The known separation device comprises in an upper part of a valve cover a raw chamber, which the contaminated blow-by gas enters, a clean chamber, out of which the cleaned blow-by gas exits, and a separating wall, which divides the raw chamber from the clean chamber. The separating wall is formed as a perforated plate so that it comprises a perforated region with multiple passage openings through which the gas from the raw chamber can flow into the clean chamber. On a wall outlet side of the separating wall facing the clean chamber, a gas-permeable separation structure of a fibre fleece covering the perforated region is arranged, which, when subjected to a through-flow, separates the particles out of the gas flow. In the case of the known separation device, a baffle wall is additionally provided, which is arranged on an outside of the separation structure facing away from the separating wall. The baffle wall is designed gas-impermeably. In the known separation device, a flow guiding structure is additionally formed on the wall outlet side of the dividing wall, which projects from the separating wall in the direction of the baffle wall. The separation structure in this case is clamped in between the baffle wall and the free ends of the flow guiding structure so that the separation structure on the one hand abuts the baffle wall and on the other hand the face ends of the flow guiding structure under preload. With the known separation device, an impactor with baffle wall is thus realised. For fixing the separation structure, pins can also project from the flow guiding structure which engage in the separation structure.
In contrast with a filter, a pure impactor is not generally subjected to a through-flow. The separation effect for solid or liquid contaminations carried along in the flow is not based on a defined pore size as with a filter but on an abrupt flow deflection and concomitant inertia effects. The separation structure is not intended to filter the contaminations out of the gas stream but only absorb and discharge if applicable the contaminations decelerated through inertia effects. For the efficiency of the particle separation of such an impactor adhering to a predetermined spacing between perforated region and baffle plate is of increased importance. Because of manufacturing tolerances, however, this spacing can vary comparatively greatly. At the same time, the compression of the separation structure with the known separation device is correspondingly varied also because of this, as a result of which the separation effect of the separation structure is also influenced. It is likewise possible in principle that the compression of the separation structure between separating wall and baffle wall because of the tolerances becomes so slight that the desired position fixing for the separation structure cannot be ensured. In addition, the preferably precise adjustment of a predetermined spacing between the perforated region and the separation structure can also have decisive influence on the achievable separation effect of the impactor.
From DE 10 2010 029 322 A1 it is known to provide openings in a valve member of a bypass valve and to cover these with a separation structure. At least with closed valve member, the openings can be subjected to a through-flow, upon which the separation structure then exhibits a certain filtering effect.
Further separation structures subjected to through-flow and consequently mainly acting as filters are known from U.S. Pat. No. 6,409,805 B1 and U.S. Pat. No. 4,627,406.